COLUMBUS, Ohio -- Despite helping coach an undefeated football team last season, Tom Herman still had his share of sleepless nights.

In his first year on the job, the Ohio State offensive coordinator helped mold quarterback Braxton Miller into the Big Ten's Offensive Player of the Year, while the Buckeyes compiled a 12-0 record in head coach Urban Meyer's first season in Columbus. Yet the thought of calling a pass play -- which ideally would make up 50 percent of the Buckeyes' offense -- kept Herman awake at night, as his confidence in Ohio State's passing game waned throughout the season.

"Literally, the thought of it sent shivers down my spine at times last year," Herman said.

With the Buckeyes ranking 105th in country in passing yards per game, Herman's fears appeared to not only justified, but solidified by Miller's pedestrian 58.3 percent completion percentage. Miller may have been his conference's top offensive player, but he often relied on his legs rather than his arm, much like the OSU offense, which ranked 10th in the country in rushing yards per game.

After 15 spring practices, Herman said that he's sleeping much better, but admitted that he still has concerns about the Buckeyes' throw-and-catch game.

"I'm not frightened to call a pass play anymore," Herman said. "Do we have to get better? Do we have to improve? Yeah. It's a little bit of a relief to be able to call that and not be so frightened."

Much of the progress that the Ohio State passing attack has made can be placed on Miller, who put an increased emphasis on improving his mechanics throwing the ball. The Buckeyes' signal-caller even spent a week of the offseason in San Diego, Calif., working out with noted quarterback specialist George Whitfield, Jr.

Miller's decision to fly out west for a week didn't go unnoticed by Herman, who also serves as Ohio State's quarterbacks coach, and was as impressed by the onus that his top player took upon himself, as he was the work that he put in with Whitfield.

"He did a good job of taking it upon himself to basically say, 'I'm going to go California for a week when we don't have bowl practices,'" Herman said. "When he came back, was he fundamentally a little bit better? Yeah, probably. As he would've been had he done anything for a week straight with football and just drills and all that stuff. I think where it helps the most to best honest with you is mentally. He feels like, 'Hey, I gave myself an advantage.'"

Real or perceived, that advantage showed up in the Buckeyes' spring game, where Miller completed 16 of his 25 pass attempts, throwing for 217 yards and two touchdowns. Showcasing improved touch on his long ball, the junior-to-be completed passes of 49 and 42 yards, in an exhibition that left his position coach feeling much better about his team's air attack.

"I was telling the rest of the staff, it's refreshing, in the spring game, it's like 100 percent pass for the Scarlet team, and it felt okay," Herman said. "We tried to do that last year in the spring game and it was a disaster. So I think that's probably the biggest thing is that it felt okay to call a pass after pass after pass."

A spring game -- which essentially doubles as a glorified scrimmage -- isn't the same setting that Miller will have to prove himself as a passer in this fall, but nonetheless, his performance can't be viewed as anything but a positive for an offense that returns nine starters from 2012. It's also helping Herman sleep better at night, especially considering where the OSU passing game stood a mere six months ago.

"We've come along way from where we were," Herman said. "As a play-caller, I don't lie awake at night with night sweats saying, 'Oh my God, I'm going to have to call this.'"